| Yulu,a salted anchovy sauce,is one of the typical products of Chinese traditional condiments.Now there are still some problems with the current production of fish sauce.The method of natural fermentation took a long period of fermentation and had much uncontrollable factors,resulting in quality was difficult to guarantee,which was a major problem for constraining fish sauce industry.Therefore,to learn the quality variation and the dynamic changes of microorganisms,and to clarify the contribution of microorganisms in fermentation to fish sauce,are good for improving the quality of the fermented fish sauce in the future.In this paper,we analyzed the flavor of the fish sauce with different salt concentrations and the succession of bacterial in the fermentation broth as well as the relationship between the bacterial and biogenic amines,in order to provide the theoretical basis for the industrial production of the fish sauce.To clarify the changing regularity of volatile flavor compounds in the early stage of fermentation of traditional fish sauce with different salt concentrations and to identify the main flavor substances,Gas chromatography-mass spectrometry(GC-MS)method was used to analyze the volatile flavor components of anchovy fish sauce broth.Fingerprints of volatile flavor compounds in the early stage of fish sauce fermentation were established.The result revealed that there were 51 and 58 common peaks in the 18% and 23% fermented fish sauce sample groups,respectively,and they were calibrated in the reference fingerprints.PCA and PLS-DA analysis demonstrate that ethanol,dimethyl sulfide,ethyl acetate,isovaleraldehyde,2-methylbutyric acid and 2,4-heptadienal were identified as differential metabolites.Ethanol,isovaleraldehyde and 2-methylbutyric acid are major volatile substances.Studies have shown that salinity has a certain selection effect on the aroma and flavour of fish sauce,and different salinity can be selected for fermentation in industrial production.The bacterial community of anchovy sauce,with 18% and 23% salt concentration was investigated by Illumina Miseq sequencing and the p H,nitrogen content and biogenic amines(BAs)were detected during the fermentation.Analysis of bacterial community showed that Enterobacter,Pseudochrobactrum,Proteus and Providencia were identified as the initially dominant genera.15 days later,Sphingopyxis,Variovorax,Reyranella and Stenotrophomonas became the most prevalent genera and the bacterial successions were significantly different depending on the salt concentration.After 45 days fermentation,Tetragenococcus predominated regardless of the different salt concentrations.Biogenic amines(BAs)dynamic changes show that spermidine and spermine were detected as the major biogenic amines and the contents of cadaverine and putrescine were relatively low throughout the fermentation.The biogenic amines varied in different salt concentration samples during the initial fermentation.However,the biogenic amines were significantly decreased(p <0.05)except for 2-phenylethylamine after 150 days of fermentation.The correlation analysis of microorganisms and biogenic amines in fermented fish sauce revealed that the abundance of dominant bacteria in the initial fermentation stage,including Pseudomonas(15.7%),Proteus(8.9%)and Providencia(22.0%)was negatively correlated with biogenic amines,especially spermidine and spermine(rs <-0.8).A multivariate statistical redundancy analysis(RDA)based on the relative abundances of bacterial community and BAs concentrations of the samples was used to systematically confirmed the relation between the dominate bacteria and BAs formation.Tetragenococcus may be the main microorganism in reducing BAs during anchovy sauce fermentation.These results not only revealed bacterial succession and dynamic changes in chemical characteristics,but also elucidated the relation between the quality characteristics and salt concentration of the Yulu fermentation. |
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